Optical 3D measurement techniques

A fast way from real three-dimensional models to a point cloud or surface or 3D-CAD models

Instead of individual points, as on a coordinate measuring machine (CMM), the 3D scanner records the entire component geometry in a high-resolution point cloud. The non-contact system delivers three-dimensional measurement data for a wide array of components, such as sheet metal, tools and moulds, turbine blades, prototypes, as well as injection and pressure die castings. For digitalising objects, an ATOS III Triple Scan System is available at the IPPE.

The scanning unit works with a projector and two optical sensors with a resolution of 8.1 MP each. Using  narrow-band blue light, the projector projects various stripe patterns phase-delayed onto the measured object. This allows very precise measurements, regardless of the lighting conditions in the environment. This point cloud is converted into a polygon mesh and describes the surface exceptionally accurately.

Fields of application:

• Digitalisation of free-form surfaces, reverse engineering into CAD models
• Nominal-actual comparison with CAD data (see below for example)
• Quality control/process monitoring
• Form and function optimisation of existing products
• Scanning of design prototypes for new product developments
• Scanning of objects which are not documented electronically for data backup (e.g.: protection of cultural property)
• Production of copies of cultural property (e.g. statues)

Optically measuring components and structures point by point (shape as well as deformation)

For the non-contact and precise measuring of 3D coordinates of selected points of an object, an optical measurement method, so-called photogrammetry, is used. Uncoded reference point markers are applied to the points to be measured. In addition, coded reference point markers are stuck or applied magnetically to and around the measurement object. Subsequently, mapping photographs are taken from all sides and from various perspectives. A reference scale is placed next to the measured object in order to determine its correct dimensions.

Fields of application:

• Measuring large objects and structures (e.g. a ship's hull)
• Point by point, quasi-static deformation analysis (before/after comparison)
• Recording of reference points for a subsequent 3D scanning process (of large measurement objects to improve measurement stability)
• Reverse engineering of components with the aid of support points
• Quick, point by point digitalisation of objects
• Optical deformation measurement

Non-contact deformation measurement of components (quasi-static or high speed)

With the optical deformation measurement system (ARAMIS), deformation of an object can be measured or, for known materials, the surface tensions calculated. The optical 3D scanner (GOM ATOS III) or two high-speed cameras (Photron SA-5) can be used for the measurement. The use of these measurement systems enables deformation measurement on components in a variety of sizes. For the measurement, a stochastic speckle pattern (fig.1) is applied to the areas of interest. Various test procedures are possible, from quasi-static to highly dynamic tests with corresponding analysis in 2D or 3D.

Fields of application:

• Material testing
• Characterisation of creeping and ageing processes
• Determination of material properties
• Examination of crack growth in fracture mechanics
• Strength assessment
• Component dimensioning
• Validation of FE models
• Analysis of the deformation behaviour of homogeneous and inhomogeneous materials
• Examination of the non-linear behaviour of components
• Determination of forming limit curves